Many agricultural formulations contain water-soluble salts of chlorinated carboxylic acid herbicides. These salts, often alkylamine salts or metal salts, are generally not as active as their acid equivalents. For example, (2,4-dichlorophenoxy)acetic acid (“2,4-D”) acid is known to be more herbicidally active than the dimethylamine salt of 2,4-D. Also, many of the chlorinated carboxylic acid herbicides are sold to the end users as esters because these esters are more active than the corresponding amine formulation. For instance, it is generally known that 2,4-D ester formulations are more effective as herbicides than 2,4-D amine formulations. The esters, however, are more likely to volatilize even after deposition onto target areas. After volatilization, these esters can cause significant damage to off-target plants.
Chlorinated carboxylic acid herbicides are usually have traditionally been reacted into amine or other salts, which are soluble in water, or into esters which are oil soluble. Both salts and esters must then break down in the environment back into the acid, which is herbicidal.
It would be preferable, then, to apply the herbicides as acids. However, they are not significantly soluble in water. Previously, solvents used to formulate 2,4-D acid such as xylene range hydrocarbons, are known to be phytotoxic to plants and may enhance herbicide volatility and subsequent drift to non-target areas. Albaugh D-638 is one such product, but it further incorporates the ester form of 2,4-D into the formulation. The formulation is 24.5% by weight of 2-butoxethyl ester of 2,4-dichlorophenoxyacetic acid (CAS #1929-73-3), 13.8% by weight 2,4-D (CAS #94-75-7) and a solvent that contains 7.7% by weight naphthalene (CAS #91-20-3). It is believed that the solvent is Aromatic 150. It is believed that solvent is present in an amount from 55 to 60%. Another commercial product containing the acid form of 2,4-dichlorophenoxyacetic acid is WEEDONE® 638 from Rhone Poulenc (now marketed by Nufarm). This formulation contains 25.2% of the 2-ethylhexyl ester of 2,4-D, 13.8% of the acid form of 2,4-D, 3% propylene glycol, 1.5% titanium oxide and other undisclosed inerts. This formulation is believed to be described in one of the following: U.S. Pat. No. 5,254,344, 5,096,711, or 5,206,021. The 2,4-D in this formulation is not solubolized, but has been dispersed through a water phase.
Another problem associated with the amine salts of some chlorinated carboxylic acid herbicides is their inability to mix with fertilizers. 2,4-D amine herbicides cannot be mixed directly into Uran (urea-ammonia nitrate) fertilizer without some dilution in water. This is a disadvantage for applicators, since this dilution practice increase the total spray volume they must apply per acre.
Surfactants are used in most agricultural formulations to enhance the ease of application. Since many pesticide formulations use hydrophobic solvents, requiring the use of surfactants to emulsify the hydrophobic solvent and pesticide into water. Surfactants have also been used both as adjuvants and formulation components to enhance the effectiveness and spreading ability of applied sprays.